Prior Art

Early Experiments

Above is my first lean steer trike
prototype. It was made from some surplus pipe that was lying
around the shed. While it did end up being too heavy, the
whole idea was to build something I could experiment with to
gain some insight into the effects of lean steer geometry. In
this trike the steering and tilting were directly connected,
so it suffered from bump steer. However an even more
pernicious problem occurred when the road you were riding on
had any sort of camber -- which most well engineered roads do
-- the trike would tend to steer towards the road center. So
in order to drive straight, the rider always needed to lean
slightly away from the center of the road. At higher speed
this caused oscillations or shimmy that ultimately effected
the high speed stability of the design. After observing this
behavior first hand, I came to realize that a successful
leaning trike must have a tilting mechanism that is
independent of the steering.

Inspiration

Much of my initital
inspiration for Jetrike came from seeing Bram Smit's <www.fastfwd.nl> tilting
trike.

On his site, he reports that his trike was
difficult to balance, and you will notice he added a caliper
brake to the rocker arm to manually lock the tilt mechanism
when stationary. My simulation
geometry would appear to confirms this. You will notice
that while most angles are 90° and the lengths are about
right, Angle A is about 120°. After estimating his setup and
simulating it, I found that the seat on his trike actually
moves in a collinear path towards the center contact patch by
12mm on a 30° tilt. Without the tilt locking caliper brake,
one would think this trike would be harder to balance than a
two wheeled inline recumbent with a similar wheelbase. People
who have actually ridden it report that its very good
cornering characteristics more than make up for requiring a
tilt lock to get started. Nevertheless, if you were planning
to replicate this design, I would make the swing arms
horizontal.

Bram Smit credits his inspiration as comming from a
Spanish builder, Carlos Calleja <www.moebius.es/ccalleja/>
and his three wheeled motorcycle prototype. Carlos was
granted US patent 5611555
for his invention in 1997.

From what I can tell, Carlos' rocker arm
has a locking mechanism that is de-activated by motion. So
when the bike is moving it is unlocked and moves freely, but
as the bike becomes stationary the mechanism locks
automatically. He also has a suspension link to the rocker
arm pivot.

Often swing arm designs are referred to as Calleja
designs, but I believe this is incorrect. The
swing arm rear end Calleja used was actually invented
and patented by Curtis L. Prince (see below) in 1987.
Meaning no disrespect to Carlos, I think these swing
arm designs should be referred to as Prince designs,
in deference to their original inventor. Only the
tilt locking mechanism and suspension configuration
should be credited to Calleja.

Key Influences

The Hipparion is a front wheel
drive (FWD) lean-steer trike built by Esko Meriluoto
<personal.eunet.fi/pp/davinci/osa5eng.html>.
This trike has negative trail and a steering dampener
to prevent dynamic instability (shimmy) at high
speeds.

The Python is a two wheeled center
steer bike invented by Jürgen Mages (pictured above)
<www.python-lowracer.de>.
Despite having negative trail, the Python geometry
provides dynamic stability by generating a self-centering
effect. I believe that free to castor (FTC) is
actually at work here.

The Speculoos is a FWD two wheeled
recumbent bike developed by Laurent Dechenne <les-velos-de-laurent.skynetblogs.be>.
It features positive trail, but according to Laurent,
to reduce pedal induced steering the bottom bracket
height must be level to the seat height and the pivot
angle should be between 55° and 60°.

This is the earliest reference I
have found to the type of tilting mechanism used in
the Jetrike design. This patent was filed by its
inventor Curtis L. Prince in 1987. Seeing we are now
in 2007 this patent has actually expired, so we are
all free to use his invention in future designs. You
will notice that the tie rods between the swing arms
and rocker arms have shock absorbers.

Ross Cowie on the Yahoo tilting
group <groups.yahoo.com/group/tilting>
brought this patent to my attention. Filed by Carling
D. Allen in 1975, it covers a swing arm design not
unlike the Prince design, only using other means
including one with pulleys (left) and others using
gears to generate the counter action in the opposing
swing arm.

A "Kurvenleger" prevented the
occupants from slipping out of their seats when
going around turns. In 1956, the Messerschmitt
studies department became involved in the further
development of the MOBO concept built in the
United States (this frontal view shows the
chassis "banked" in a left turn.

Messerschmitt designed this Tilter with
trailing/leading arms in 1956. This is the earliest
swing arm design I am awear of, but it is unclear
from the photo, what form of counter action is
employed by this design.

Other Tilting Trikes

This patent was filed by a Swedish
builder, Björn Häggkvist in 1975. It is an
interesting FWD design where the seat and drive train
form one frame, and the delta rear end another. The
steering pivot itself is driven by a sprocket on the
handle bar stem. This approach eliminates pedal
induced steering, but the problem with this design,
like many other lean steer trikes is that the rider
center of gravity (CoG) appears to move outward as
the trike turns.

This patent was filed
by Roger H. Feikema and Harry J. Bakker in 1982.
Trailmate <www.trailmate.com>
manufacturers these under the name 'Fun Cycle' and 'Banana
Peel' and they are marketed as an industrial bike for
the tourist bike rental market. A British company
Trixstar <www.trixstar.co.uk> also made an
identical looking trike (pictured above).

The Vacuum Velocipede was invented by
Dave E. Berkstresser, who filed his patent in 1982.
This trike was way ahead of its time, and although it
never set any speed records, it certainly is a unique
speed machine. With a very low steering pivot angle
it reportedly suffered from serious wheel flop, in an
attempt to fix this, a linear drive was added to
lower the CoG of the riders legs.

This patent was filed
by William P. Mason in 1995 and the trike went into
production under the name 'Tricumbent Raven'. From
what I understand, Tricumbent have ceased trading and
the IP is now owned by Just Two Bikes <www.justtwobikes.com>
who sell a very similar trike called the 'Tricumbent'.

While the rear wheel steer delta trike is
considered by most to be unstable, a prolific home
builder, Timothy Smith <www.ihpva.org/people/tstrike/home.htm>
who has built one, is quoted on his web sit as saying:
"if I had only 1 machine it would be this".

This is Wayne Soohoo's
<www.maxmatic.com/soohoo.htm>
very cool Aileron tilting trike. His trike has a
special ratcheting spring clutch in the handle bar
stem that controls the tilt lock. As I understand it,
tipping the handle bar to the side, activates the
clutch, and a spring pushes the tilting bike back to
center. It is a very interesting concept, and from
the perspective of stability, his tilting tadpole
trike should have better stability than a delta,
because the CoG is more central to the intersection
of the contact patches. I only wish he had had more
commercial success with it. His patent was filed in
1995.

This is patent was
filed by William J. Stites of Stites Design <www.stitesdesign.com>
in 1996 for his Chameleon leaning three wheeled HPV.
For such an interesting and beautifully realized
design, the drawings in the patent application are
rather ordinary.

Alan Maurer invented
this leaning trike that features steering modulation
control. This is an inspired design. You control the
lean by pushing side to side on the handle bars. At
the same time you control how much the lean
influences steering by pitching the handle bars
forward and back. The only potential problem with
this design is that the breaking torque on the front
wheels is transferred to these steering controls.
Alan entered the trike in 2002 HPV Championship <www.ihpva.org/Races/ihpsc28_res.html>
held at Brantford, Ontario, Canada. Here are some
detailed photos of the front and rear. His
patent was filed in 2001.

This is a design
patent filed in 2001 by Robert Ridley and Eric
Jackson of APAX Vehicle Developments Inc <www.apax.ca>. These
are some crazy trike builders -- they have a video
where they literally ride it down a set of stairs (above).
But I wonder just how much that air suspension
actually weighs. On this bike, when you stop, you
still have to press a button to lock the tilt
mechanism.

Conclusion

Looking at all these inventors and their patents, one
wonders if filing a patent is really worth it. Few if any of
these trike designs have been a commercial success, and the
whole patent filing process takes time and resources away
from a fledgling business at a critical stage in its
development. By comparison Greenspeed in Australia and
Catrike in the US have been a huge success, by building
brands not protecting intellectual property. This only
reinforces my belief in open design. My personal view is that
business success does not come from innovative technology so
much as capturing a market for it -- and that comes down to
marketing.

Whether you acknowledge it or not, we all stand on each
others shoulders, so I encourage you to share what you know
-- no matter how insignificant you might think it is -- it
may just be that missing piece of the puzzle that helps
someone else realize their dream and make it a reality.